Many integrated circuits (ICs) are alterable, or configurable, at various stages of manufacture to yield different variations of a basic IC. This is an efficient and economical manufacturing practice. One disadvantage of conventional manufacturing methods is that some ICs can be configured or reconfigured after manufacture by unauthorized persons. As a result the IC may be damaged, the IC may not function appropriately for its intended use, or other unintended and undesirable consequences may result. It is therefore desirable to be able to configure or reconfigure an IC at various stages of manufacture, or after manufacture, in a manner that is efficient, secure, and provides the maximum amount of configuration flexibility.